It has been intended to provide a letterpress type printing machine using a relatively viscous ink which, after being applied to the printed web or sheet, is quickly dried by being cured through exposure to ultraviolet light. Such a machine is sold by Arpeco Engineering Ltd., 5265 Creekbank Road, Mississauga, Ontario, Canada.
In such a prior art letterpress, the system provides, among other features, an upright ink fountain that delivers ink, under gravity, onto and across the width of a rubber form roller. The said roller uses a relatively soft rubber surface having a hardness reading of about 50 Shore A durometer reading, measured on the rubber hardness scale. A doctor blade was provided, set at an angle of 90 degress to the roller's surface so as to be adapted to be selectively advanced radially of the axis of the roller, with the purpose and intent of indenting the surface of the rubber roller to an extent sufficient to control the thickness of the ink that was carried by and on the surface of the rubber roller past the indenting edge of the doctor blade.
Practical experience with the foregoing machine, which is known as a letterpress printing press, had established that during high speed operations, the rubber form roller for the ink would burn up, causing destruction of the roller and requiring substantial down time for the machine to permit substitution of a new roller for the destroyed roller. Additionally, it was observed that the ink could not be properly metered consistently for the intended result, and the rubber roller could not be maintained properly for its intended life while operating at maximum intended production rate. Alternatively, such a machine was required to be operated at less than maximum production speed, which meant that the per unit cost of production of the printed material was substantially increased.
It was also observed that the color of the printed material on different copies of a batch of printed copies would vary, which was undesirable.
In an attempt to correct the deficiencies in the machine, as are noted above, it was postulated that the burn up, or destruction, of the rubber form roller was being caused by the development of heat at the surface and in the body of the rubber roller, resulting from an energy loss brought about by the doctor blade being required to indent the rubber surface moving at a relatively high speed; and that such heat could not be properly dissipated when the printing press was to be operating at its intended high output rate.
It was further postulated that use of a rubber roller as a form roller, coupled with a doctor blade as above described, failed to provide a system that could accurately meter ink delivered to the printing plate on a consistent basis for all production speeds of the machine.
It was further postulated that the ink was being so churned, or affected, within the ink fountain by the movement of the rubber form roller and/or by the interaction of said form roller and doctor blade, that the viscosity of the ink was being altered locally to an extent sufficient to effect color change in the layer of ink being deposited from the rubber form roller onto the printing plate and thence onto the work.
It was, therefore, decided to redesign the aforesaid machine, and to improve such machine, so as to avoid the said problems incident to usage of the existing machine.
One object of this invention is to provide an arrangement which permits a printing press of the type described to function properly at all speeds including maximum speed, whereby the per unit cost of production of printed material could be reduced, and the cost effectiveness of the printing press could be optimized.
Another object of this invention is to provide, in a printing press, an improved means for transferring to the printing plate only a desired amount of printing ink that is to be dried by exposure to ultraviolet light.
A further object of this invention is to provide, in a printing press, an improved means for transferring from an ink fountain, and for transporting by roller, only a desired amount of printing ink for use with the type of printing machine disclosed, so as to avoid the problems of producing printed material with variations in the color of the print thereof.
Further objects and advantages of this invention will be made known to persons skilled in the art, through the following specifications which describe and disclose my invention.